[PATCH 04/25] fs: super: introduce the functions to get super by cdev reference

[Dongsheng Yang <yangds.fnst@cn.fujitsu.com>]

As we have cdev in super block now, we can provide get_super_cdev
to get super_block by a cdev reference, similar with get_super
which is working only for block_device.

Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
---
 fs/super.c         | 45 +++++++++++++++++++++++++++++++++++++++++++++
 include/linux/fs.h |  2 ++
 2 files changed, 47 insertions(+)

diff --git a/fs/super.c b/fs/super.c
index 928c20f..4a9031a 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -605,6 +605,37 @@ rescan:
 
 EXPORT_SYMBOL(get_super);
 
+struct super_block *get_super_cdev(struct cdev *cdev)
+{
+	struct super_block *sb;
+
+	if (!cdev)
+		return NULL;
+
+	spin_lock(&sb_lock);
+rescan:
+	list_for_each_entry(sb, &super_blocks, s_list) {
+		if (hlist_unhashed(&sb->s_instances))
+			continue;
+		if (sb->s_cdev == cdev) {
+			sb->s_count++;
+			spin_unlock(&sb_lock);
+			down_read(&sb->s_umount);
+			/* still alive? */
+			if (sb->s_root && (sb->s_flags & MS_BORN))
+				return sb;
+			up_read(&sb->s_umount);
+			/* nope, got unmounted */
+			spin_lock(&sb_lock);
+			__put_super(sb);
+			goto rescan;
+		}
+	}
+	spin_unlock(&sb_lock);
+	return NULL;
+}
+EXPORT_SYMBOL(get_super_cdev);
+
 /**
  *	get_super_thawed - get thawed superblock of a device
  *	@bdev: device to get the superblock for
@@ -628,6 +659,20 @@ struct super_block *get_super_thawed(struct block_device *bdev)
 }
 EXPORT_SYMBOL(get_super_thawed);
 
+struct super_block *get_super_cdev_thawed(struct cdev *cdev)
+{
+	while (1) {
+		struct super_block *s = get_super_cdev(cdev);
+		if (!s || s->s_writers.frozen == SB_UNFROZEN)
+			return s;
+		up_read(&s->s_umount);
+		wait_event(s->s_writers.wait_unfrozen,
+			   s->s_writers.frozen == SB_UNFROZEN);
+		put_super(s);
+	}
+}
+EXPORT_SYMBOL(get_super_cdev_thawed);
+
 /**
  * get_active_super - get an active reference to the superblock of a device
  * @bdev: device to get the superblock for
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 2f1d9499..5c7d789 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2744,7 +2744,9 @@ extern void get_filesystem(struct file_system_type *fs);
 extern void put_filesystem(struct file_system_type *fs);
 extern struct file_system_type *get_fs_type(const char *name);
 extern struct super_block *get_super(struct block_device *);
+extern struct super_block *get_super_cdev(struct cdev *);
 extern struct super_block *get_super_thawed(struct block_device *);
+extern struct super_block *get_super_cdev_thawed(struct cdev *);
 extern struct super_block *get_active_super(struct block_device *bdev);
 extern void drop_super(struct super_block *sb);
 extern void iterate_supers(void (*)(struct super_block *, void *), void *);
-- 
1.8.4.2